Staphylococcus aureus is one of the most common causes of nosocomial bloodstream infections and is also an important cause of endocarditis, osteomyelitis, and other infections. Antibiotic resistance in S. aureus is a serious clinical problem that is compounded by the ability of the organism to form a biofilm on human tissues and inserted medical devices such as catheters. Most strains of S. aureus are able, under the appropriate environmental conditions, to elaborate a surface-associated (3-1-6-linked polymer of N-acetyl-glucosamine (PNAG) that serves two significant virulence functions: 1. it functions as the major constituent of the biofilm exo-polymeric matrix and 2. it protects the bacteria from phagocytosis during infection. The development of a biofilm during infection often results in a bacterial population that is refractory to antimicrobial chemotherapy and can act as a smoldering nidus for relapsing infection. In addition, resistance to phagocytosis enables the bacteria to evade the immune system. Therefore, it is not surprising that the intercellular adhesin (ica) locus, which encodes four proteins, Ica A, IcaD, IcaB, and IcaC, that are involved in PNAG synthesis, appears to play a critical role in virulence. Current therapeutic modalities for S. aureus infections could be significantly improved by inhibiting the formation of a resistant biofilm. The long-term objective of this project is to characterize the regulation of PNAG elaboration and subsequent biofilm formation bv S. aureus. A thorough understanding of this pathway could lead to the identification of targets for anti-biofilm therapeutic agents to act svnergisticallv with conventional antibiotics. This addresses the Healthy People 2010 goal of fighting "Infectious Diseases and Emerging Antimicrobial Resistance" and goal 14-20 "Hospital Acquired Infections". We have isolated an RNA-binding protein that binds to ica transcript and appears to increase half-life of the RNA and inhibit translation. The immediate goal of this proposed project is to further characterize the post- transcriptional regulatory mechanism bv which this RNA-binding protein regulates ica expression and PNAG production. Short Description. Staphylococcus aureus is an important pathogen that can cause a variety of infections. Antibiotic resistance in S. aureus is common and the problem is compounded by its ability to form adherent, polysaccharide-encased communities called biofilms. The goal of our research is to characterize the mechanism by which biofilm formation is regulated in S. aureus. Understanding the mechanism of biofilm regulation could lead to the development of anti-biofilm therapies that would act synergistically with conventional antibiotics.